Police forces in England and Wales have gathered data on millions of people who have called to report possible crimes or pass on information, it was revealed yesterday.

In some cases, staff not only recorded names, addresses and contact details, but asked about the callers' date of birth and ethnicity. Senior officers admitted details could be used in future investigations but insisted their databases were needed to fight crime, protect vulnerable people and ensure concerns were dealt with appropriately.

The forces revealed personal information was spread across up to 22 databases, saying details of the same person could be recorded several times. They said staff and officers were following guidance published by the National Policing Improvement Agency.

West Midlands police, the second largest force, holds 1.1m records of people who have reported offences over the past 12 years. Lancashire, Cleveland, Avon and Somerset, Gloucestershire, West Mercia and North Wales hold more than 150,000 each.

Thirteen forces responded, but most said it was not possible to do so because the scale of the task was so big.

Daniel Hamilton, of the pressure group Big Brother Watch, said: "For the police to log this kind of information isn't just wrong – it's dangerous.

"The public must be confident that, when they report a crime, they do so in the comfort of anonymity and without risk of their details being stored on a central police database which can be accessed by thousands of people."

Ian Readhead, director of information at the Association of Chief Police Officers, said forces should only record information relevant to the call.

An "amicable exchange of information" could be used against callers in the future, but most people would expect police to hold on to it.

"What is important is that data is retained in applications that are clearly transparent and subject to audit and that the information commissioner is content with the business processes. We must be transparent and reassure the public that the information is not being misused."